1 Field of the Invention
The present invention relates to the production of bacterial capsular polysaccharides and their use for the production of conjugate vaccines.
2 Description of the Related Art
The first step in making a vaccine is to separate the disease-making, from the immune-inducing activity. In practice this means isolating or creating an organism, or part of one, that is unable to cause full-blown disease, but that still retains the antigens responsible for inducing the host's immune response.
We distinguish two major groups of vaccines: whole organism vaccines and sub-unit vaccines. Whole organism vaccines are produced by killing/inactivating or attenuating/weakening organisms. Sub-unit vaccines include vaccines based on for example protein antigens and carbohydrate antigens.
Anti-bacterial vaccines produced using carbohydrate antigens may be composed of a purified (capsular) polysaccharide from the disease-causing organism. Examples of such vaccines are: Haemophilus influenzae type b (Hib), Neisseria meningitidis (A, C, W and Y), Salmonella typhi (Vi), and Streptococcus pneumoniae (23 different serotypes) polysaccharide vaccines.
Polysaccharide vaccines appeared not to protect infants under 2 years of age and not to induce long term T-cell memory. Therefore, a new generation of conjugated polysaccharide vaccines was introduced. Conjugate vaccines appeared to be immunogenic in young children and induce a long-term memory. Conjugate vaccines are mainly produced by attaching the polysaccharide to a protein carrier.
The first conjugate vaccine that was introduced worldwide was directed against Haemophilus influenzae type b (Hib). Haemophilus influenzae type b causes pneumonia and meningitis, mostly in young children.
It spreads by droplet through coughs, sneezing and in overcrowded living conditions. It is estimated to cause 2 to 3 million cases of disease each year and about 450,000 deaths, the vast majority of them in developing countries.
Several vaccines against Hib are already in widespread use in high-income countries, where they have virtually wiped out the disease. The vaccines are among the safest now in use. Studies have confirmed the effectiveness of these vaccines in low-income countries, but relatively few of them have begun routine use in infants. Hib vaccine is one of the most under-utilized vaccines because of its relatively high cost in comparison with the vaccines routinely used in the regular childhood immunization program.
The production processes used nowadays are relatively expensive, and include a long cultivation step of about 16-18 hours, see e.g. U.S. Pat. No. 4,644,059 and the period for culturing is typically based on arbitrary parameters, such as time or optical density, see e.g. U.S. Pat. No. 4,220,717. In this way, it is not possible to compensate for changes in culture conditions and suboptimal yields of polysaccharide are the inevitable result. In addition, harsh chemicals such as phenol are used to recover the polysaccharide, see e.g. U.S. Pat. No. 4,695,624 and EP 0 528 635.
In order to contribute to the goal of the WHO (World Health Organization) and GAVI (Global Alliance for Vaccines and Immunization), to make Hib conjugate vaccine available for all children in the world and in order to give people in developing countries a chance to get access to Hib-technology, a relatively simple and easily up-scalable production process has to be developed, patented and licensed to these countries under reasonable terms. The vaccine produced should meet the relevant WHO requirements.